If kids have to save the grown ups, then they have a strong bargaining position to e.g. fix the climate ASAP. => Why don't they use it?
What are they supposed to bargain with? They are (as a population, individuals may be exceptions to this) fundamentally dependent upon the adult population for their existence. Food, shelter, clothing, transportation is all (in the US) provided by adults for the vast majority of kids, at least below age 16, and still the majority for most 16/17 year olds. If we permit 18-20 year olds to still be counted as "kids", they are still poor and a very small voting bloc that is notorious for not showing up to vote, even if they are increasingly independent.